Sphygmometer



March 14, 1967 F. N. GILLETTE ET AL 3,308,811

SPHYGMOMETER Filed March 30, 1964 5 Sheets-Sheet 2 37 38 39 PUMP UPSYSTOLE DIASTOLE FIG; 2

SI 52 53 54 55 58 59 46W 14w Mr SHAPER SMOOTHER FF FF FROM 7 7 AMP. 29

62 W F/ 6 3 OUTPUTS PUMP uP QUIET SYSTOLE DIASTOLE F IG. 4

INVENTORS FRANK N. GILLETTE JOHN w. GRAY BY ARVID w. JACOBSON ATTORNEY.

March 14, 1967 Filed March 30, 1964 F. N. GILLETTE E l.

SPHYGMOMETER 5 Sheets-Sheet 5- ATTORNEY.

March 14, 1967 GlLLETTE ET AL 3,308,811

SPHYGMOMETER' Filed March 30, 1964 5 Sheets-Sheet 4 r. L FROM Ldclc CKT32 ISI I 34 INVENTORS FRANK N. GILLETTE JOHN w. GRAY BY ARVID w.JACOBSON ATTORNEY.

March 14, 1967 F. N. GILLETTE ET AL 3,308,811

SPHYGMOMETER 5 Sheets-Sheet 5 Filed March 30, 1964 N? .56 JOmkZOo 20mmmm C6 5528 205 EN EMILE 20mm INVENTORS FRANK N. GILLETTE JOHN W. GRAY BYARVID W. JACOBSON ATTORNEY.

United States Patent 3,308,811 SPHYGMOMETER Frank N. Gillette and JohnW. Gray, Pleasantville, and Arvid W. Jacobson, Millwood, N.Y.,assignors, by mesne assignments, to Smith Kline & French Laboratories,Philadelphia, Pa, a corporation of Pennsylvania Filed Mar. 30, 1964,Ser. No. 355,610 10 Claims. (Ql. 1282.05)

This invention relates to apparatus for automatically determining thesystolic and diastolic blood pressure of a human subject.

It is well known that arterial blood pressure varies during the cycle ofeach heart beat between a maximum value called the systolic pressure anda minimum value called the diastolic pressure. In the most commonpresent technique -for determining blood pressure the physician wraps apressure cuff around the patients upper arm and raises the pressure inthe cufl to a level above the systolic blood pressure of the patientthereby cutting oil the flow of blood completely. He then allows thepressure to diminish slowly and as it diminishes listens with astethoscope to the sounds originating in the artery below the point ofcutoil. At the same time he observes pressure on a manometer or othersuitable gauge connected to the cuif. At the highest pressure there isno blood fiow through the artery and there is no sound. When thepressure falls below the systolic blood pressure level, blood flowsthrough the constriction at the maxima of the heart pressure pulses. Asthe pressure reduces further, blood flows throughout a larger and largerportion of the pressure cycle. Finally, when the pressure is lower thanthe diastolic blood pressure the artery is open through the entire cycleand blood flow is uninhibited.

During this pressure cycle the physician hears nothing at all above thesystolic level. He hears pulses which vary in amplitude and characterwhen the pressure lies between systolic and diastolic levels. He againhears nothing when the pressure is below the diastolic point.

At a pressure level a few millimeters above the diastolic pressure thesound changes in character acquiring a mufiled characteristic that iseasily detectable by a skilled physician. The pressure at which thisOccurs is generally termed the onset of muflling.

According to all common practice the pressure level at which the firstsound is heard is called the systolic pressure. The diastolic point isdefined either as the cessation of sound or as the onset of mufilingdepending upon the conviction of the physician taking the readings.

Machines have been made in the past to read blood pressureautomatically. In general, they have included the usual cuff and-amanual or automatic pump which inflates the cuff to occlude the artery.A typical machine includes two pressure gauges to monitor the pressurein the cuff, each including a valve which may be closed at anappropriate time to hold the indicator constant. The stethoscope isreplaced by a microphone which generates pulse signals as blood passesthrough the stoppage. The output of the microphone is amplified, passedthrough a filter to minimize extraneous sounds such as the rustling ofclothing, and passed to a control circuit. The latter circuit respondsto the occurrence of the first pulse to close the valve to the systolicguage and responds to a cessation of pulses to close the valve to thediastolic 3,398,811 Patented Mar. 14, 1967 gauge. The difficulty with amachine of this kind is that it responds solely to cessation of soundrather than to the onset of muflling and correspondingly no combinationof amplifier gain and threshold setting provides correct results for allsubjects.

It is a general object of the present invention to provide an improvedsphygmometer for detecting systolic and diastolic pressurer Anotherobject is to provide a sphygmometer which consistently gives the sameresults as obtained by a physician even when operated by a technician.

A more specific object of the invention is to determine by automaticmeans the pressure corresponding to the onset of mufiling and to presentthis as the diastolic pressure.

Briefly stated, the invention is based on the discovery that the soundsindicative of systolic and diastolic pressures lie in differentfrequency bands. Accordingly, the invention includes the usual pump,cuif and microphone for monitoring sounds. The output of the microphoneis passed through a filter which passes a first band of frequenciesuntil the systolic point is determined whereupon the characteristics arechanged so as to pass a second band of frequencies which enables thediastolic point to be determined more accurately. Additionally, if thesound level is unusually high, as it is for some patients, the gain ofthe system is automatically reduced after the systolic point has beenpassed.

For a clearer understanding of the invention reference may be made tothe following detailed description and the accompanying drawing inwhich:

FIGURE 1 is a schematic block diagram of the apparatus in accordancewith the invention;

FIGURE 2 is a diagram useful in explaining the invention;

FIGURE 3 is a schematic block diagram of the logic circuit shown inFIGURE 1;

FIGURE 4 is a table showing the operation of the logic circuit;

FIGURE 5 is a schematic diagram of the logic circuit shown in FIGURES 1and 3;

FIGURE 6 is a schematic diagram of the high pass filter and controlcircuit; and

FIGURE 7 is a schematic diagram of the amplifier and control circuit.

Preliminary investigation of the problem has shown that the sound ofinterest lies in a band of frequencies from 30 to c.p.s. Detection ofthe systolic pressure is comparatively easy because the sounds representthe difference between no noise and some noise. The diastolic pressureis more difiicult to detect because it is not a sharply defined point.The only criterion for operation is that the machine shall give the sameresult as is obtained by a physician. A more thorough investigation hasled to the following observations:

(1) All of the energy of interest for the determination of both thesystolic and diastolic points is transmitted through a sharp cutofffilter with its normal end points at 30 and 100 c.p.s.

(2) The diastolic point is the pressure at the onset of muffiing andafter the onset of mufiling the energy that would pass through a sharpcutoff filter .with the end points lying at 50 and 100 c.p.s. is verysmall. There remains significant energy below 50 c.p.s. and it is thiswhich must be ignored by a machine to detect the onset.

of mufiling.

(3) At the systolic point the pulses have not enough energy in thenarrower band for dependable detection. The total energy down to the 30c.p.s. cutoff is required.

(4) Some individuals have a very high sound level. For these, the energypassing through the narrow filter after the onset of mufiling may stillbe enough to fool the machine. For such subjects a reduction in systemgain appears desirable.

Some persons develop a very low signal level for quite a while after thesystolic point. All of the energy in the pulse is required fordependable operation in this region.

From the above observations it has been concluded that a satisfactorymachine must operate in the following manner:

(1) There must be a narrow band filter having its upper end point at 100c.p.s.

(2) ,The filter must have two end points at the low end, one at 30c.p.s., the other at 50 c.p.s., with means for switching between them.

(3) The machine must have fairly high gain to work reliably with lowinput levels.

(4) There must be means for reducing the gain in the presence of a veryhigh level input.

, (5) At the start of a reading the gain must be high and the filtermust be set to the 30 c.p.s. end point.

(6') When the systolic point is reached the filter end point must shiftto 50 c.p.s., but after a delay sufiicient to cover the period of lowsignal level mentioned above.

(7) If a high amplitude signal appears and holds for two or three pulsesthe gain must switch to a level perhaps one-third or one-half of maximumand must stay at the low level until the diastolic point has beendetected.

Referring now to FIGURE 1 there is shown the usual cuff 11 wrappedaround the arm 12 of a patient. Positioned within the cuff beyond thepoint of occlusion is a microphone 13 which monitors the sounds of bloodthrough the artery and generates signals indicative thereof. A pipe 14connects the cuff to a suitable pump such as the usual bulb 15 used toinflate the cuff. A relief valve 16 may be opened after full pressurehas been attained so as to release the pressure at a uniform rate. Alsoconnected to the pipe 14 is a pressure responsive actuator 17 which isconnected to two switches 18 and 19. When the pressure rises to a lowvalue such as 15 low pass filter 26 having a cutoff frequency f in therange from eighty to one-hundred twenty cycles per second, which ispreferably 100 c.p.s. The filter 26 is connected to a high pass filter27 the cutoff point of which is normally at a frequency f in the rangefrom twenty to forty cycles per second, preferably about 30 c.p.s. butwhich may be switched by application of a suitable signal from a controlcircuit 28 to have a cutoff frequency of f in the range from forty tosixty cycles per second, preferably about 50 c.p.s. The output of thefilter 27 is connected to an amplifier 29 the gain of which may beswitched from a high value to a low value upon application of a suitablesignal from a control circuit 31. The amplifier 29 is connected to alogic circuit 32 which generates suitable output signals on theconductor 33, 34, 35 and 36 as will be more fully explained.

Referring now to FIGURE 2 there is shown schematically the sequence ofoperations. When the pump 15 is operated the microphone 13 generatessignals shown by the waveform 37 due to the fiow of air into the cuffand these signals continue until the end of pump-up when a period ofquiet follows, indicated by the line 38. The relief valve 16 is openedat this time allowing the pressure to fall gradually until a point isreached in which blood spurts through the stoppage. The pressure at thispoint is the systolic pressure. Flow continues in spurts as the pressureis further decreased causing additional signals to be generated as shownby the waveform 39 until a point is reached at which the sounds, irfheard in a stethoscope, would begin to be muffled. The pressure at thistime is the diastolic pressure.

Referring again to FIGURE 1, as soon as power is applied by theoperation of the pump 15, the actuator 17 and the switches 18 and 19, awarning lamp 41 is illuminated. At the end of pump-up the logic circuit32 generates a signal on the conductor 33 which actuates a lamp controlcircuit 42 which extinguishes the lamp 41 and also generates a signal ona conductor 43 which is passed to the control circuit 31. When thesystolic point is reached the logic circuit 32 generates two signals,one on conductor 34 and one on conductor 35 indicative of this point. Itwould be possible to utilize but a single control signal but in theparticular circuit being described millimeters of mercury, the actuator17 closes the switches 18 and 19 thereby connecting the batteries 21 and22 into the circuit to activate the machine.

Two pressure gauges 23 and 24 are also connected to the pipe 14 and areprovided to indicate systolic and diastolic pressure respectively. Eachof these gauges is of the kind whose indication may be locked at anytime upon the application of suitable signals. One suitable kind isdescribed in the copending application of John W. Gray, Arthur F. Hayekand Arvid W. Jacobson, Jr., Ser. No. 313,351, filed Oct. 2, 1963, forLockable Meter, which application is assigned to the same assignee as isthe instant application. Briefly, the cited application describes apressure gauge provided with an electromagnet which attracts a magneticdisk fastened to the pointer shaft and clamps it to the frame therebylocking the indicator. Such an arrangement is illustrated schematicallyin FIG. I wherein electromagnets 23' and 34' are shown mechanicallyconnected to the gauges 23 and 24 respectively.

The microphone 13 is connected to an amplifier 25 the principal purposeof which is to provide a. low impedance source for the signals generatedby the microphone 13. The amplifier 25 is connected to a bandpass filterwhich passes a band of frequencies extending from either one of twolowfrequency limitsto a highfrequency limit. As shown in FIGURE 1 thebandpass filter comprises a two complementary signals have been found tobe con-.

venient and accordingly two are shown. The signal on the conductor 35operates a drive circuit 44 which controls the electromagnet 23 which inturn locks the systolic gauge 23. The systolic signal on conductor 34 isdelayed by about five seconds by a time delay circuit 45 after Which asignal is passed by a conductor 46 to the control circuit 28. Uponreceipt of this signal the control circuit 28 actuates a switchingmechanism in the filter 27 which changes the cutoff point from f to fthat is, from 30 to 50 c.p.s. Additionally the control circuit 28gencrates an enabling signal on the conductor 47 which is passed to thecontrol circuit 31. The control circuit 31 is inactive until it hasreceived signals from both the conductor 43 and the conductor 47whereupon it becomes active. The output of the gain control amplifier 29is: also connected to the control circuit 31, and, if the signal exceedsa predetermined amplitude, a switching circuit within the amplifier 29is operated so as to reduce the gain by a factor of two.

At this point the systolic pressure has been indicated, the cutoff pointof the filter 27 has been switched and, it the signal is at a highlevel, the gain of the amplifier 29 has been reduced. Signals continueto flow to the logic circuit until the diastolic point has been reachedwhereupon a signal on the conductor 36 operates a drive circuit 49 whichcontrols the electromagnet 24' which in turn locks the diastolicpressure gauge 24.

FIGURE 3 shows the logic circuit in block diagram form. The signals fromthe amplifier 29 are irregular in form as indicated by the waveform 51.These signals are applied to a shaping circuit 52 the function of whichis to generate a series of pulses of uniform width and uniform amplitudeas indicated at 53. The circuit 52 may be a conventional monostablemultivibrator in which each of the irregular pulses 51 triggers thecircuit to its unstable state. The circuit reverts to its stable stateafter a time delay determined by the constants of the circuit which inthis case may be approximately one-quarter of a second. Such amultivibrator circuit is well known and need not further be described.

The pulses 53 are applied to a smoothing circuit 54 the function ofwhich is to generate a single long pulse such as the pulse 55 as long asthe train of pulses 53 continues and which ends upon an interruption inthe train of pulses 53. This circuit will be more fully described. Thepulses 51, 53 and 55 occur during pump-up and similar pulses also occurduring the period between the systolic and diastolic point.

The pulse 55 is applied to a flip-flop circuit 58 which is triggered toone of its states by the leading edge of the pulse 55 and is triggeredto its opposite state by the trailing edge of the pulse 55. Theflip-flop 58 is connected to a second flip-flop 59 and triggers thissecond flip-flop only upon the completion of a full cycle of operationof the flip-flop 58.

FIGURE 4 indicates the condition of the flip-flops 58 and 59 at varioussteps of operation. The flip-flop 58 initially has outputs 0, 1 onconductors 61 and 62 respectively and this condition continues until theend of pumpup whereupon conditions are reversed. The condition of theflip-flop 58 again reverses at the systolic point and yet again at thediastolic point as indicated in FIGURE 4. The flip-flop 59 has outputsof 0 and 1 on conductors 63 and 64 respectively during both the pump-upand quiet periods. At the systolic point the conditions reverse and theconductors 63 and 64 carry outputs of 1 and 0 respectively for theremainder of the cycle as indicated in FIGURE 4.

Referring now to FIGURE 5, there is shown the shaping circuit 52 theoutput of which is coupled by a capacitor 71 to the smoothing circuitwhich consists essentially of the transistors 72 and 73 and theirassociated circuitry. The collector of the transistor 72 is connectedthrough a resistor 74 to the negative source; the base is connectedthrough a resistor 75 to the positive source; and the emitter isconnected through a resistor 76 to the positive source. The collector ofthe transistor 73 is connected through a resistor 78 to the negativesource; its base is connected directly to the collector of thetransistor 72 and its emitter is grounded. A capacitor 79 couples theemitter of the transistor 72 to the base of the transistor 73. Anauxiliary transistor 81 has its collector and emitter connectedrespectively to the collector and emitter of the transistor 73. Thetransistor 81 is normally nonconductive and consideration of itsoperation will be deferred.

When the power is first turned on the transistor 72 would benonconductive except that at the same time a negative-going signal fromthe shaping circuit 52 turns the transistor 72 on. The collector 72 isnear ground potential and the transistor 73 is nonconductive. Thecapacitor 79, being short circuited through the transistor 72, isdischarged. Upon the passage of the first pulse 53 and before the nextpulse arrives the transistor 72 becomes nonconductive and the capacitor79 starts to charge. However, the parameters of the circuit are selectedso that the capacitor 79 does not charge sufficiently to turn on thetransistor 73 before the arrival of the next pulse at which time thecapacitor 79 is again discharged through the transistor 72. Thus thecollector of the transistor 73 remains at a negative potential as longas the pulses 53 continue to arrive. Thus a long pulse waveform 55 isgenerated. However, interruption in the train of pulses 53 allOWs thecapacitor 79 to charge sufiiciently to render transistor 73 conductivethereby terminating the pulse 55.

The pulse 55 is coupled by a capacitor 82 to the flipfiop circuit 58which consists essentially of the transistors 83 and 84 and theirassociated circuitry. These transistors are connected as a conventionalflip-flop circuit. The leading edge of the pulse 55 turns 011? thetransistor 83 and turns on the transistor 84. The two previouslymentioned output conductors 61 and 62 are connected to the collectors ofthe transistors 83 and 84 respectively.

The flip-flop 59 consists of the transistors 86 and 87 and theirassociated circuitry. These transistors are also connected in aconventional flip-flop circuit. However there is an auxiliary transistor88 the collector of which is connected to the collector of thetransistor 86 and the emitter of which is connected to the emitter ofthe transistor 86. The base of the transistor 88 is connected throughserially connected resistors 91 and 92 to a source of positivepotential. The junction of the resistors 91 and 92 is connected througha capacitor 93 to a source of negative potential. When power is firstapplied the resulting transient is passed through the capacitor 93 tothe base of the transistor 88 thereby turning it on. Since the collectorof the transistor 88 is connected to the collector of the transistor 86which is coupled to the base of the transistor 87 the transistor 86 isalso initially turned on while the transistor 87 is initially cut oft".This condition is indicated in FIGURE 4.

Returning to FIGURE 5 the collector of the transistor 83 is coupled by acapacitor 94 to the anodes of two diodes 35 and 06 the cathodes of whichare connected to the collectors of the transistors 86 and 87respectively. By this well known connection a negative-going change inthe potential of the collector of transistor 83 has no effect While apositive-going change flips the transistors 86 and 87 to the oppositestate. Such a positive-going change occurs at the systolic point asindicated in FIG- URE 4. The previously mentioned output conductors 63and 64 are connected to the collectors of the transistors 86 and 87respectively.

The first output signal required of the logic circuit is that requiredto turn off the lamp 41 (FIGURE 1). The conductors 62 and 64 areconnected to the anodes of diodes 101 and 102 respectively the cathodesof which are connected together and through a resistor 103 to thenegative source. It is obvious that as long as both the conductor 62 andthe conductor 64 are negative no current will flow through the resistor103 and the potential of the conductor 33 will be negative. When eitherone of the conductors 62 or 64 becomes positive (in the present case theconductor 22 becomes positive) current will flow through the resistor103 thereby placing a positive potential on the conductor 33 whichoperates through the lamp control circuit 42 to turn off the lamp.

The next signal required of the logic circuit is the systolic signal.This occurs when the conductors 63 and 64 change their polarityconditions. The conductor 64 is connected directly to the conductor 35and generates a positive-going signal at the systolic point whichoperates through the drive circuit 44 to lock the systolic gauge. Theconductor 63 is connected directly to the conductor 34 and provides anegative-going signal which is passed to the time delay circuit 45.

The next signal required is the diastolic signal and this occurs whenthe conductors 62 and 64 both become positive. The conductors 62 and 64are connected to the cathodes of diodes 104 and 105 respectively theanodes of which are connected together and through serially connectedresistors 106 and 107 to a source of positive potential. The conductor36 is connected to the junction of resistors 106 and 107. It is obviousthat as long as either one of the conductors 62 and 64 is negative, current will flow through the resistors 107 and 106 causing low potentialto appear on the conductor 36. However, when both of the conductors 62and 64 become positive, current flow ceases and a positive-going signalappears on the conductor 36 which is applied to the drive circuit 49which in turn locks the diastolic gauge.

Finally, the logic circuit generates another signal at the diastolicpoint which is the complement of the just described signal and isobtained from the conductors 61 and 63. These conductors are connectedto the anodes of the diodes 108 and 109 respectively the cathodes ofwhich are connected together and through a resistor 111 to a source ofnegative potential. A capacitor 112 is connected to the cathodes of thediodes 103 and 199 and to a source of positive potential. It is obviousthat as long as one of the conductors 61 or 63 is positive, current willflow through the resistor 111 making the potential of the conductor 113at or slightly above ground potential. However, when both the conductor61 and the conductor 63 are negative, current fiow ceases and a negativesignal is applied to the conductor 113 which is connected to the base ofthe transistor 81 thereby rendering this transistor conductive,short-circuiting the transistor 73 and preventing passage of any furtherpulses.

Referring now to FIGURE 6 the high pass filter 27 is shown as one typeof active filter, that is, a filter including an amplifier withfrequency selective feedback. The amplifier comprises the transistors121 and 122. Input signals from the low pass filter 26 are coupledthrough capacitors 123 and 124 to the base of the transistor 121, thecollector of which is connected through a resistor 125 to a source ofnegative potential. The base of the transistor 121 is connected througha resistor 126 to ground; the emitter is connected through a resistor127 to ground. The collector of the transistor 121 is connected directlyto the base of the transistor 122 the emitter of which is grounded. Avoltage divider comprising serially connected resistors 128, 129 and 131is connected between a source of negative potential and a source ofpositive po tential. The collector of the transistor 122 is connected tothe junction of resistors 128 and 129. The collector of transistor 122is also coupled by a capacitor 132 to the amplifier 29. A resistor 133is connected between the collector of transistor 122 and the junction ofcapacitors 123 and 124. The cutoff frequency of the filter may bechanged by altering the values of the resistors 133 and 126. This isaccomplished in effect by means of a resistor 134 which has one terminalconnected to the lower end of the resistor 133 and the other terminalconnected to the collector of transistor 135 the emitter of which isconnected to the upper end of the resistor 133. In a similar fashion, aresistor 136 is connected to the upper terminal of the resistor 126 andto the collector of the transistor 137 the emitter of which is connectedto the lower terminal of the resistor 126. When the transistors 135 and137 are nonconductive the resistors 126 and 133 alone are in the circuitwhile when these transistors are conductive the resistors 133 and 126are effectively reduced in value by having the resistors 134 and 136respectively connected in shunt with them. The transistors 135 and 137are normally nonconductive and the cutoff frequency of the filter is 30c.p.s. When these transistors are made conductive the cutoff frequencyis shifted to 50 c.p.s.

The conductivity of the transistors 135 and 137 is controlled by thecondition of a flip-flop circuit comprising the transistors 141 and 142.The collector of the transistor 141 is connected through a resistor 143to ground while the collector of transistor 142 is connected through aresistor 144 to the source of negative potential. The emitters areconnected together and through resistor 145 to a source of positivepotential. The base of the transistor 141 is returned to the positivesource through a resistor 146 while the base of the transistor 142 isconnected through a resistor 147 to the positive source. The collectorof the transistor 141 is coupled by a resistor 148 to the base of thetransistor 142. v

The conductor 34 from the logic circuit 32 carries a negative-goingsignal when the systolic point is reached.

8 This signal is delayed in time by the time delay circuit 45 whichconsists of a resistor 151 and capacitor 152 serially connected from theconductor 34 to the source of positive potential. The output conductor46 of the time delay circuit is connected to the junction of theaforesaid resistor and capacitor. Prior to the systolic point, theconductor 46 carries a positive potential which is applied to the baseoi the transistor 141 rendering this transistor nonconductive andrendering the transistor 142 conductive. Accordingly, the collector ofthe transistor 142 is at or slightly above ground potential therefrommaintaining the transistors and 137 nonconductive. When the systolicpoint is reached, the negative-going signal of the conductor 34 startsto charge the capacitor 152 so that the potential of the conductor 46starts to fall. circuit is large so that the potential of conductor 46does not become sufficiently negative to turn on the transistor 141 forapproximately five seconds after the systolic point has been reached.Then the transistor 141 is made conductive and the transistor 142 ismade nonconductive; the potential of the collector 142 becomes negative;and the transistors 135 and 137 are made conductive thereby insertingthe resistors 134 and 126 into the circuit and changing the cutofi pointof the filter from 30 c.p.s. to 50 c.p.s. The collector of thetransistor 142 is also connected to the conductor 47 so that anegative-going signal is passed to the control circuit 31.

Referring now to FIGURE 7, there is shown a schematic diagram of thecontrol amplifier 29 and the control circuit 31. The amplifier comprisesessentially the transistor 161, the base of which is coupled by thecapacity 132 to the output of the filter 27. The base of the transistor161 is returned to ground through a resistor 162 while the emitter isconnected through a resistor 163 to a source of negative potential. Thecollector is also connected directly to the base of the transistor 164which acts as emitter follower. The collector is connected directly tothe source of negative potential while the emitter is connected througha resistor 165 to a source of positive potential. A capacitor 166 isconnected between the base of the transistor 164 and ground. The emitterof transistor 164 is coupled by a capacitor 167 to the logic circuit 32.

The gain of the transistor 161 is controlled by the amount ofdegeneration caused by unbypassed emitter resistors. More specifically,the emitter of the transistor 161 is connected through a resistor 168 tothe positive potential source. The emitter is also connected through theserial combination of a capacitor 171 and a resistor 172 to ground. Aresistor 173 has one terminal connect- 7 ed to the junction of capacitor171 and the resistor 172 and the other terminal connected to thecollector of atransistor 174 the emitter of which is grounded. The baseof the transistor 174 is connected through a resistor 175 to asource ofpositive potential. The transistor 174 is normally conductive therebyeffectively shunting the resistor 172 with the resistor 173. Theresistors 168, 172 and 173 are all in the emitter circuit of thetransistor 161 and are unbypassed thereby causing degeneration. When thetransistor 174 is made nonconductive the resistor 173 is removed fromthe circuit thereby increasing the amount of resistance in the emittercircuit, increasing the degeneration and thereby decreasing the gain ofthe stage.

The control circuit 31 consists essentially of two transistors 181 and182 connected as a conventional flip-flop circuit. At the end of thepump-up period a negativegoing signal on conductor 43 from the controlcircuit 42 is applied through resistor 183 to the base of the transistor182 thereby rendering this transistor conductive. The transistor 181 isthereby rendered nonconductive and its collector is at a negativepotential which potential is passed by a resistor 184 to the base of thetransistor 174 thereby rendering the latter transistor conductive andholding thegain of the amplifier to its higher value.

As previously mentioned the amplifier gain should be increased fiveseconds after the-passage of the systolic The time constant of thepointprovided that the signal level is above a predetermined magnitude atthis time. This is accomplished by applying the signal to a summingpoint 185. The junction 185 is connected through a resistor 186 to asource of positive potential and is also connected to the cathode of adiode 187 the anode of which is connected to the base of the transistor181. The negative-going signal on the conductor 47 from the controlcircuit 28 occurs approximately five seconds after the systolic point isreached and is passed through a resistor 188 to the summing point 185.Additionally, a signal from the output of the amplifier is coupled by acapacitor 189 to the summing point 185. In the absence of thenegative-going signal on the conductor 47 the amplifier output can neverbe of sufficient amplitude to pass through the diode 187 to the base ofthe transistor 181 to such an extent as to render the transistor 181conductive. However, the signal from the control circuit 28 lowers thepotential of the summing point 185 sufficiently so that if the output ofthe amplifier exceeds a predetermined magnitude the potential of thejunction 185 can become sutficiently negative to pass through the diode187 to the base of the transistor 181 thereby rendering this transistorconductive. When this occurs the collector of the transistor 181 risesin potential and this rise is passed to the base of the transistor 174thereby turning it off, removing the resistor 173 from the circuit anddecreasing the gain of the amplifier by a factor of two.

The signal from the lamp control circuit 42 prepares the circuit foroperation by turning onthe transistor 182. Thereafter, five secondsafter the passage of the systolic point as indicated by the signal fromthe control circuit 28, the gain of the amplifier can be reducedprovided the signal level exceeds a predetermined magnitude.

From the foregoing description it is apparent that applicants haveprovided a novel and effective sphygmometer. The energy of the signalsfrom the microphone contained in a first band of frequencies, from about30 c.p.s. to about 100 c.p.s., is used to determine the systolicpressure. Since some individuals exhibit a low signal level for a whileafter the systolic point has been reached, this first band is utilizedfor several seconds thereafter, whereupon the frequencies utilized arelimited to a second band from approximately 50 c.p.s. to approximately100 c.p.s. The diastolic point is determined as the pressure existing atthe onset of mufiling which is manifested by the absence of energy inthis second, more limited band. More specifically, the absence of energyin this limited band (not the complete absence of output from themicrophone 13) causes an interruption of the pulses 53 which in turnterminates the long pulse 55 thereby triggering the flip-flop 58 to itsfinal condition. Additionally, if the patient is one of thoseindividuals who exhibit very high level signals, the gain of theamplifier is reduced.

Apparatus according to the invention has been built and tested on manydifferent persons and has been found to give results in close agreementwith the results obtained by a physician using a stethoscope.

Although a specific embodiment of the invention has been described inconsiderable detail for illustrative purposes, many modifications willoccur to those skilled in the art. It is therefore desired that theprotection afforded by Letters Patent be limited only by the true scopeof the appended claims.

What is claimed is:

1. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone for monitoring the sounds of arterial flow past said cuffand generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normallypassing a first band of fre- It? quencies in the range of from thirty toone-hundred cycles per second and selectively actuable to pass a secondband of frequencies in the range of from fifty to one-hundred cycles persecond,

means responsive to the first occurrence of a signal passing throughsaid filter means as the pressure in said cufi is reduced for recordingthe pressure then existing in said cuif and for actuating said filter topass said second band of frequencies, and

means responsive to a subsequent interruption of the signal passingthrough said filter for recording the pressure then existing in saidcuff.

2. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from thepoint of occlusion for monitoring the sounds of arterial flow past saidcuff and for generating electrical signals in response thereto, and

a filter receiving signals generated by said microphone for normallypassing a first band of frequencies in the range of from thirty to onehundred cycles per second and selectively actuable to pass a second bandof frequencies in the range of from fifty to one-hundred cycles persecond, 7

a control circuit connected to the output of said filter,

said circuit including means responsive to the first occurrence of asignal passing through said filter as the pressure in said cuff isreduced for recording the pressure then existing in said cuff and foractuating said filter to pass said second band of frequencies,

said circuit also including means responsive to a subsequentinterruption of the signal passing through said filter for recording thepressure then existing in said cuff.

3. A sphygmometer, comprising:

a cutf for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from thepoint of occlusion for monitoring the sounds of arterial flow past saidcuff, where-by as the pressure is reduced said microphone generates afirst series of electrical pulses each indicative of a spurt of bloodpassing through said artery,

filter means receiving signals generated by said microphone, whereby theoutput of said filter means is a second series of electrical pulses,

said filter means normally passing a first band of frequencies in therange of from thirty to one hundred cycles per second and beingselectively actuable to pass a second band of frequencies in the rangeof from fifty to one-hundred cycles per second, and

a control circuit connected to the output of said filter means,

said circuit including means responsive to the occurrence of the firstpulse of said second series of pulses for recording the pressure thenexisting in said cuff and for actuating said filter means to pass saidsecond hand of frequencies,

said circuit also including means responsive to a subsequentinterruption in said second series of pulses for recording the pressurethen existing in said cuff.

4. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuff slowly,

a microphone positioned adjacent to said artery downstream from thepoint of occlusion for monitoring the sounds of arterial flow past saidcuff and for generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normallypassing a band of frequencies between a first predetermined lowerfrequency below which there is no sound energyof interest and apredetermined upper frequency above which there is no sound energy ofinterest and being selectively actuable to raise said firstpredetermined lower frequency representative of the onset of mufiling toa second predetermined lower frequency, and

a control circuit connected to the output of said filter means,

said circuit including means responsive to the first occurrence of asignal passing through said filter means as the pressure in said cuif isreduced for recording the pressure then existing in said cult and foractuating said filter to pass said second band of frequencies,

said circuit also including means responsive to a subsequentinterruption of the signal passing through said filter means forrecording the pressure then existing in said cuff.

5. Apparatus according to claim 4 in which said first predeterminedlower frequency is in the range from twenty to forty cycles per second,said second predetermined lower frequency is in the range from forty tosixty cycles per second, and said predetermined upper frequency is inthe range from eighty to one hundred and twenty cycles per second. i

6, Apparatus according to claim 4 in which said first predeterminedlower frequency is approximately thirty i cycles per second, said secondpredetermined lower frequency is approximately fifty cycles per second,and said predetermined upper frequency is approximately one hundredcycles per second.

7. A sphygmometer, comprising: a cuif for encircling a portion of thehuman body, means for inflating said cuff to occlude an artery, meansfor reducing the pressure in said cuff slowly, a microphone positionedadjacent to said artery downstream from the point of occlusion formonitoring the sounds of arterial flow past said cuff and for generatingelectrical signals in response thereto, filter means receiving signalsgenerated by said microphone for normally passing a first band offrequencies in the range of from thirty to one-hundred cycles per secondand selectively actuable to pass a second hand of frequencies in therange of from fifty to one-hundred cycles per second, a control circuitconnected to the output of said fiiter means, saidcircuit includingmeans responsive to the first occurrence of a signal passing throughsaid filter means as the pressure in said cutf isredu-ced for generatinga first control signal, means responsive to said first control signalfor recording the pressure then existing in'said cuff, means fordelaying said first control signal, means responsive to the signal sodelayed for actuating said filter means to pass said second band offrequencies, said control circuit also including means responsive to asubsequent interruption of the signal passing through said filter meansfor generating a second control signal, and means responsive to saidsecond control signal for recording the pressure then existing in saidcuff. 8. A sphygmometer, comprising: a end for encircling a portion ofthe human body, means for inflating said cud to occlude an artery, meansfor reducing the pressure in said cuff slowly, a microphone positionedadjacent to said artery downstream from the point of occlusion formonitoring the sounds of arterial flow past said cuff and for generatingelectrical signals in response thereto, filter means receiving signalsgenerated by said microphone for normally passing a first band offrequencies'which passes all sound energy of interest and selectivelyactuable to pass a second band of frequencies which excludes soundenergy below that frequency required to detect the onset of mufiiing. anamplifier connected to the output of said filter means, normallyinactive means for reducing the gain of said amplifier when the outputthereof exceeds a predetermined magnitude,

means responsive to the first occurrence of a signal passing throughsaid amplifier as the pressure in said cufi is reduced for the triplepurpose of recording the pressure then existing in said cuff, foractuating said filter means to pass said second hand of frequencies, andfor activating said normally inactive means, and

means responsive to a subsequent interruption of the signal passingthrough said amplifier for recording the pressure then existing in saidcuff.

9. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for inflating said cuff to occlude an artery,

means for reducing the pressure in said cuif slowly,

a microphone positioned adjacent to said artery downstream from thepoint of occlusion for monitoring the sounds of arterial fiow past saidcult and for generating electrical signals in response thereto,

filter means receiving signals generated by said microphone for normallypassing a first band of frequencies which passes all sound'energy ofinterest and selectively actuable to pass a second band of frequencieswhich excludes sound energy below that frequency required to detect theonset of mufiiing.

an amplifier including switch means operable to reduce the gain thereofconnected to the output of said filter means,

a control circuit connected to the output of said amplifier,

said circuit including means responsive to the first occurrence of asignal passing through said amplifier as the pressure in said cuff isreduced for generating a first control signal,

means responsive to said first control signal for recording the pressurethen existing in said cuff.

means for delaying said first control signal to generate a secondcontrolsignal,

means responsive to said second control signal for actuating said filterto pass said second hand of frequencies,

means jointly responsive to said second control signal and to the outputof said amplifier in excess of a predetermined magnitude for operatingsaid switch means,

said control circuit also including means responsive to a subsequentinterruption of the signal passing through said amplifier for generatinga third control signal, and means responsive to said third controlsignal for recording the pressure then existing in said cuff.

10. A sphygmometer, comprising:

a cuff for encircling a portion of the human body,

means for selectively inflating said cufi to occlude an artery,

means for relieving the pressure in said cufi slowly,

first and second pressure gauges each for indicating the pressure withinsaid cuff,

each of said gauges including means for locking its indication despitesubsequent pressure changes,

a microphone for monitoring the sounds of arterial flow past said cuif,whereby as the pressure is relieved said microphone generates a firstseries of electrical pulses each indicative of a spurt of blood passingthrough said artery, 7

a bandpass filter operatively connected to the output of saidmircophone, whereby the output of said filter is-a second series ofelectrical pulses.

said filter having characteristics normally pasing a band meansresponsive to an interruption in said second of frequencies between afirst predetermined lower series of pulses for locking said secondgauge. frequency below which there is no sound energy of interest and apredetermined upper frequency above References Cited by the Exammelwhich there is no sound energy of interest and in- 5 UNITED STATES A S3112125235!Z5 2$223325? iliimifiiiiwii $101,082 8/1963 Seen at 128-105fre uenc to d d t (11 f 3,140,710 7/1964 Glassner et a1. l282.05

q y e representative of the onset of mufiling, means responsive to theoccurrence of the first pulse of 10 ROBERT MORGAN Acting PrimaryExaminer.

said second series of pulses for locking said first gauge and foractuating said selectively actuable SIMON BRODER Exammermeans, and

1. A SPHYGMOMETER, COMPRISING: A CUFF FOR ENCIRCLING A PORTION OF THEHUMAN BODY, MEANS FOR INFLATING SAID CUFF TO OCCLUDE AN ARTERY, MEANSFOR REDUCING THE PRESSURE IN SAID CUFF SLOWLY, A MICROPHONE FORMONITORING THE SOUNDS OF ARTERIAL FLOW PAST SAID CUFF AND GENERATINGELECTRICAL SIGNALS IN RESPONSE THERETO, FILTER MEANS RECEIVING SIGNALSGENERATED BY SAID MICROPHONE FOR NORMALLY PASSING A FIRST BAND OFFREQUENCIES IN THE RANGE OF FROM THIRTY TO ONE-HUNDRED CYCLES PER SECONDAND SELECTIVELY ACTUABLE TO PASS A SECOND BAND OF FREQUENCIES IN THERANGE OF FROM FIFTY TO ONE-HUNDRED CYCLES PER SECOND, MEANS RESPONSIVETO THE FIRST OCCURRENCE OF A SIGNAL PASSING THROUGH SAID FILTER MEANS ASTHE PRESSURE IN SAID CUFF IS REDUCED FOR RECORDING THE PRESSURE THENEXISTING IN SAID CUFF AND FOR ACTUATING SAID FILTER TO PASS SAID SECONDBAND OF FREQUENCIES, AND MEANS RESPONSIVE TO A SUBSEQUENT INTERRUPTIONOF THE SIGNAL PASSING THROUGH SAID FILTER FOR RECORDING THE PRESSURETHEN EXISTING IN SAID CUFF.